Eye Diagram Mask Test

Use mask testing to verify that a displayed Eye Diagram complies with an industry-standard waveform shape. A mask is a template that consists of pass/fail regions on the PLTS display screen. The input waveform must remain outside the fail regions in order to comply with the industry standard. Any acquired data point that falls inside a fail region appears in red and is logged as a mask test failure.

In this topic:

Eye Diagram Mask Testing

By default, limit line PASS | FAIL testing is ON. The Meas tab displays running totals of the number of waveforms sampled and number of failed samples.

Click on the Plot Toolbar to turn ON and OFF both the Eye Mask and the PASS | FAIL text.
The PASS | FAIL text (alone) can be turned ON and OFF with a User Preference. Learn how.

Create an Eye Mask

There are two ways to create an Eye mask in PLTS:

Limit Mask Definition Pane - Simple with limited settings (shown below).
Define Eye Mask Dialog - More comprehensive method.

Important Note: The ONLY way to apply an Eye Mask to a Eye Diagram is using the Import button on the Limit Mask Definition Pane, regardless of the method that was used to create or edit the Eye Mask.

The Limit Mask Definition Panel

Use the Limit Mask Definition pane to quickly create a simple Eye diagram mask for Pass/Fail testing.

In this dialog, you can also Import a previously-defined Eye Mask.

1. On the Limit Mask Definition Pane, click Create

Refer to this diagram for the following descriptions:

Limit Mask Definition dialog box help

Dialog appearance for *.xml or *.msk (DCA) masks

This is the default appearance of the Limit Mask Definition panel.

Dialog appearance for *.mskx (FlexDCA) masks

When importing an NRZ mask or drawing/selecting a PAM4 eye diagram plot, the Limit Mask Definition panel changes, as shown below.

Adjusting Mask Scale

Scaling parameters adjust the absolute position of the mask.

Scaling Activates the following controls:

Position - X-axis left-most location of mask

Delta T - X-axis width of mask

Logic 0 Level - Minimum voltage of logical 0. Voltages below this value will fail.

Logic 1 Level - Maximum voltage of logical 1. Voltages above this value will fail.

Note: when an Eye Mask was defined using ratios (in the Define Eye Mask dialog) a preference can be set when importing the Eye Mask to set the Logic 0 and Logic 1 levels to the measured values. Learn more.

Adjusting Mask Tolerance Parameters

Changes the shape of the center mask. Orange lines on the display indicate how the selected parameter will be adjusted.

When importing a different shape (4 or 8 point) some of these settings can NOT be adjusted.

Jitter Delta T (X1)

Slope Delta T (X1)

One Y1

Zero Y2

Eye Height Y1 (Y2, Delta Y)

Buttons

Create - Create a new eye mask. Learn more.

Import - Click to import a mask file. Learn more.

Delete - Deletes current eye mask.

Save - Saves ALL of the mask settings to a *.xml file.

Apply - Applies changes to mask scale and tolerance settings.

Mask Test Scaling

Scaling supports changing the eye mask position.

Delta T - X-axis width of mask.

Horizontal Alignment The following controls adjust the horizontal position of the mask:

Automatic - Predefines the Alignment Method to "NRZ Eye" or "PAM Eye" whenever a PAM4 eye diagram is loaded.

Manual - Manually set the horizontal position in picoseconds.

Vertical Alignment The following controls adjust the vertical position of the mask:

Automatic - For NRZ, predefines the Alignment Method to "Eye Boundaries (align to One, Zero Levels)." For PAM4, predefines the Alignment Method to "Display (Align to VTop, VBase)."

Manual - Manually set the Logical 1 Level and the Logical 0 Level in millivolts. (Not available for PAM4 eye diagrams.)

Mask Test Margins

Show and adjust test margins. Learn more.

Mask Test Margins On - Displays the test margins in a lighter gray than the mask.

Manual Mask Margin Value - Adjusts test margin with either a positive or negative value.

Buttons

Import - Click to import a mask file. Learn more.

Delete - Deletes current eye mask and, for imported NRZ masks, returns the Limit Mask Definition pane to its default appearance and functions.

Import (Open) an existing mask

Click to import a mask with one of the following file formats:

PLTS	*.xml	Create, import, and save.
DCA	*.msk	Import only.
FlexDCA	*.mskx	Import only. Supports NRZ and PAM4.

Importing an NRZ mask or drawing/selecting a PAM4 eye diagram plot changes the appearance and available functions of the Limit Mask Definition panel. Learn more above.

PLTS installs a library of FlexDCA eye mask files (*.mskx) on your PC in ...\Documents\Keysight PLTS 2023 (64-bit)\EyeMasks\FlexDCA_Masks. Most of the folders within this library provide NRZ mask files. PAM4 mask files reside in the "Open Eye" folder.

Note: Once a mask is imported, it is immediately applied to the selected plot. If it does not appear, click on the Plot Toolbar to turn ON and OFF both the Eye Mask and the PASS | FAIL text.

After opening a mask, PLTS positions the mask parameters as follows:

Mask position - the mask’s horizontal center is aligned to the plot horizontal center
Logic 1 level - this value is read from Automated Eye Diagram Measurement Results.
Logic 0 level - this value is read from Automated Eye Diagram Measurement Results.

When the mask test starts, PLTS automatically aligns the mask to the waveform data on the display graticule. If there is more than one eye diagram on the display graticule, the mask aligns to the first zero-crossing point.

Use the Vertical scale controls to adjust the display for optimal viewing. Learn more.

Limit Mask Margins for FlexDCA

Mask margins are used to determine the margin of compliance for a standard or scaled mask. Margins indicate areas that are to contain a specified number of hits (violations within the mask region) in order to comply with testing standards. You can use this information to determine by what level the waveform begins to fail to comply with industry standards. Mask regions are shown in dark gray, and mask margins are shown in light gray. Any acquired data point that falls inside a mask margin appears in red. You can specify positive or negative margins:

Positive margins determine how much larger you will be able to increase the mask size before violations occur. Enter between –100% and +100% linear change in mask size.

Negative margins determine how much smaller you have to decrease the mask size before violations no longer occur. Enter between –100% and +100% linear change in mask size.

Positive Margin Value	Negative Margin Value

Define Eye Mask Dialog

There are two ways to create a new mask in PLTS:

Limit Mask Definition Pane - Simple with limited settings (shown above).
The following Define Eye Mask Dialog -is a more comprehensive method.

Click Tools, then Define Eye Mask

Define Eye Mask dialog

Define the shape and values of the Eye Diagram Mask. Measured values outside the shaded area will be flagged as a failures.

1. Select Defining Mode

Choose the method of defining the diagram:

Define by ratios The mask is created using values that are relative to 1. For example, for an applied pulse width of 400 ps, and an x-axis value is .8, the equivalent absolute setting is 320 ps.
Define by inputting time and amplitude values The mask is created using time and voltage.

2. Define the Top, Middle, and Bottom of Mask

Top Region

All eye data should be less than ...(mv). The maximum expected value. Voltages exceeding this value will fail.

Middle Region The size and shape of the Eye diagram Mask.

4 (point) vertex or 6 (point) vertex.
Horizontal Symmetry When checked, the left and right halves are forced to be mirror images. When cleared, specify all data points in the vertex.
Values Define X/Y axis values of each point in the selected shape. The grid ID value corresponds to the point on the plot starting at the far left and continues clockwise as shown in the above image.

Bottom Region

All data should be greater than ... Enter the minimum expected value. Levels below this value will fail.

3. Save and Recall

Stores the Eye Diagram Mask to an *.xml file, or Recall a previously created Eye Diagram Mask for editing.

Save by ratios - The mask is saved and recalled or applied using ratio data.
Save by time and voltage - The mask is saved and recalled or applied using time and voltage data.

Import this Eye Mask using the Limit / Mask Definition pane.

Last Modified:

6-Dec-2022	Enhancements with 2023
2-Jan-2013	Enhancements with 2013
21-Oct-2011	New topic